Added NPM to project, moved JS logic from HTML pages to external JS files

[meekg33k]

• Added npm to project for ease of local development.
• Added a simple Express server to serve Safe Paths app locally and aid faster development.
• Refactored Location Scrubber and Publisher pages, moved JavaScript logic from internal <script> tags external files in public directory as part of foundational work needed for future changes like adding linter to the project.
• Updated README to include details about running the app locally.